Female garibaldi damsellishHypsypops rubicundusstrongly prefer to spawn with males guarding early-stage eggs over those guarding empty nests or nests with late-stage eggs. According to the parental investment hypothesis, such female behavior is an adaptive response to male egg-guarding tactics which are dependent on brood size and age, and result in brood size and age-dependent differences in clutch hatching success. In this study, I tested five predictions derived from this hypothesis, along with the underlying assumption that males experience a trade-off between egg guarding and self-maintenance activities. Feeding rates of nesting males declined when males received eggs and remained low until late in the brood-cycle. Thus, males experience a trade-off between egg guarding and feeding. Males nearly always cannibalized the entire brood when they received only a singleclutch, and the probability of cannibalism of last clutches increased with brood age. Males were also more attentive of larger bloods and guarded them more aggressively. These behaviors would result in higher hatching success of eggs deposited among other early-stage eggs.